Method of producing casting moulds for precision casting

ABSTRACT

A method of producing casting moulds for use in the precision casting, in which a slurry of refractory material is prepared by mixing a powdered refractory material, a binder obtained by the hydrolysis of ethyl silicate with an amount of water smaller than the theoretical hydrolysis amount, and a small amount of a gelling promoting agent, said slurry of refractory material being poured into a shaping mould, and after said slurry has gelled in said shaping mould, the resultant casting mould is removed from said shaping mould and immersed in a hardening water containing a surface active agent or a water-soluble silicasol or both therein, whereby said casting mould is completely hardened, following which said hardened casting mould is dried and calcined.

United States i atent 1 Ultumoto et al,

1541 11 1181111011) 011 PRODUCHNG CASTKNG MQULDS 1 0R PRECESHON CASTHNG [75] Inventors: Talteorni Ultumoto, Kamalcura;

liiroshi Ueda, Kashiwa; Junji Sakai, Tokyo; Yoga Shimada, Matsudo, all of Japan [73] Assignee: Hitachi, Ltd, Tokyo, Japan [22] Filed: Mar. 19, 1973 [21] Appl. No.:342,4110

[30] Foreign Application Priority Data Mar. 21, 1972 Japan 47-27394 [52] US. Cl 106/383, 106/3835, 106/389, 164/15, 164/25 [51] llnt. Cl E281) 7/34 [58] Field of Search 106/383, 38.35, 38.9; 164/15, 25

[56] References Cited UNlTED STATES PATENTS 3,423,216 1/1969 Somers 106/383 [451 Mar. 11, 1975 3,686,006 8/1972 Horton 106/383 3,752,631 8/1973 Moore 106/383 3,769,044 10/1973 Horton 106/383 Primary Examiner-Lorenzo B. Hayes Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT A method of producing casting moulds for use in the precision casting, in which a slurry of refractory material is prepared by mixing a powdered refractory material, a binder obtained by the hydrolysis of ethyl silicate with an amount of water smaller than the theoretical hydrolysis amount, and a small amount of a gelling promoting agent, said slurry of refractory material being poured into a shaping mould, and after said slurry has gelled in said shaping mould, the resultant casting mould is removed from said shaping mould and immersed in a hardening water containing a surface active agent or a water-soluble silicasol or both therein, whereby said casting mould is completely hardened, following which said hardened casting mould is dried and calcined.

33 Claims, N0 Drawings METHGD F PRODUCING CASTlNG MOULDS FOR PRECISHON CASTING This invention relates to a method of producing casting moulds for precision casting, using a flowable refractory slurry.

It is well known that a casting mould producing method is widely being used at the present time, which comprises pouring a flowable refractory slurry into a shaping mould, removing the resultant moulding from said shaping'mould after the poured slurry has solidified, and rapidly heating the surface of. said moulding to form micro-cracks therein and thereby to increase the dimensional accuracy of the product mould and render the surface of the mould smooth and flat.

in the casting mould producing method described above, however, a burner or firing (self-calcination) is used as drying means for rapidly heating the surface of the product casting mould removed from the shaping mould and, when the casting mould has a groove or hole whose depth is larger than twice of the width or diameter thereof, the flame does not reach the bottom of said groove or hole and thus it is impossible to heat the casting mould rapidly and uniformly. Consequently, cracks occur at the portions where the flame does not reach, which degrade substantially the dimensional accuracy and quality of the product castings.

Further, in the prior art method micro-cracks are formed in the surface layer of the casting mould by rapidly heating said surface layer. but the formation of these microcracks, on one hand. substantially degrades the strength of the casting mould. For this reason, the method of producing casting moulds only with a flowable refractory slurry is applicable only to the production of casting moulds having specific shapes and cannot be applied to the production of casting moulds having complicated shapes, such as a core mould used in' the investment casting.

it is, therefore, the object of the present invention to provide a method of producing casting moulds for precision casting, which overcomes the above-described disadvantages of the prior art method and enables the application range of the product casting to be expanded and the quality and dimensional accuracy thereof to be enhanced.

In order to achieve the object set forth above, ac cording to the present invention there is provided a method which comprises preparing a flowable refractory casting material by mixing a powdered refractory material with a binder obtained by the hydrolysis of ethyl silicate with an amount of water smaller than the theoretical hydrolysis amount and a small amount of a gelation promoting agent. pouring the casting material into a shaping mould, removing the resultant casting mould from the shaping mould after said poured casting material has solidified, immersing the casting mould in a hardening water containing a surface active agent or a water-soluble silica sol or both to completely harden said casting mould, and then drying and cal'cining said casting mould, whereby the final product of casting mould is obtained.

in the present invention, ethyl silicate is generally used as a binder in the form of an alcoholic solution. The principal reaction in this case is hydrolysis ofethyl silicate. In case of tetramer of ethyl solicate 40 which is frequently used as a binder, the reaction scheme is as follows:

As may be understood from the above scheme. 14.7 g of water is required per g of ethyl silicate 40 for the complete hydrolysis of ethyl silicate 40. To use ethyl silicate as binder is to make use ofthe transformation ofthe reaction system from so] to gel in the process of hydrolysis. Describing the transformation in detail, the hydrolysis of ethyl silicate is represented by the following scheme:

l Sl DC H5 H 0 SI]. OH C H OH In this case, the following condensation reaction takes places concurrently:

The alcohol (CQHsOH) and water (H O) formed by this condensation reaction are removed from the casting mould and finally SiO- remains by which the casting mould is tightly bound.

In the preparation of the flowable refractory slurry by use of the completely hydrolyzed solution of ethyl silicate 40 and in the operation of moulding a casting mould by pouring said slurry into a shaping mould, the method of gelling the flowable refractory slurry and removal of alcohol remaining in the casting mould has a large influence on the swelling and occurrence of cracks in the casting mould.

In the present invention, the gelling is promoted and the removal of remaining alcohol is effected by immersing the casting mould in water to which a surface active agent or a water-soluble silica so] or both is or are added, and an ethyl silicate solution which is prepared with an amount of water less than necessary for the complete hydrolysis of ethyl silicate is used as the binder.

The theoretical amount of water necessary for the complete hydrolysis of ethyl silicate 40 is about 15 percent by volume as stated above. When the solution prepared with an amount of water less than this amount (hereinafter this solution will be referred to as a partially hydrolyzed binder), is left tostand overnight, the following phenomenon is observed which is not observed in a completely hydrolyzed solution of ethyl silicate 40:

Namely, when water is added to the partially hydrolyzed binder, highly tacky SiO particles precipitate immediately and then the binder is gelled and solidified.

In case of the completely hydrolyzed solution of ethyl silicate, the solution is diluted as being transparent and the entire solution is gradually gelled and solidified as being transparent, when water is added thereto.

The reaction between the partially hydrolyzed binder and water is not known, but it is assumed that, since the amount of water is small at the time of hydrolysis, the residual groups such as OH and OC H are present in the solute in a highly active state and induces successively hydrolysis reaction and condensation reaction when contacted with water, thus causing the abovedescribed phenomenon. Unless water is added. this partially hydrolyzed binder is stable in its state of sol even when it is left to stand still for several months in a sealed condition.

The casting mould producing method of this invention takes advantage of such a characteristic of the partially hydrolyzed binder as described above. In practicing the method, a flowable refractory slurry is prepared by adding a powdered refractory material to the partially hydrolyzed binder and poured into the shaping mould, with a small amount of a gelling promoting agent added thereto. The resultant casting mould is immersed in the aforesaid water (hereinafter referred to as hardening water) concurrently when the binder begins to gel, whereupon the casting mould is gelled and hardened rapidly from the surface thereof. In this case, the alcohol formed in the casting mould dissipates into the hardening water so vigorously as can be recognized through visual observation. Since the condensation reaction proceeds in the presence of a sufficient amount of water, the molecules become larger according to the scheme given below, while binding the particles of re fractory material rigidly, and thus, the strength of the casting mould is increased.

l I -Si-OH- -Si-O-Sil I Further, the hardening of the casting mould is effected by the contact reaction between the liquid and the surface of the casting mould, so that the casting mould is hardened concurrently from the entire surface thereof, and therefore, a casting mould of any desired shape can be produced with high accuracy and with no defects such as swell'or cracks which are usually caused by complicacy in shape and size of a desired casting mould. 4

The following method is employed for facilitating the management of the casting mould characteristics and moulding operation based on the above-described production principle of casting moulds:

A flowable refractory slurry is prepared by adding a powdered refractory material to the partially hydrolyzed binder and then a small amount of a gelling promoting agent is added thereto. As the gelling promoting agent. ammonium carbonate, triethanolamine, pyridine and piperidine are usually used but any other compounds may also be used, provided that they will render the pH of the partially hydrolyzed binder basic and promote gelling of the slurry.

The amount of the gelling promoting agent added is so selected that gelling will commence in about 6-8 minutes after the slurry is poured into the shaping mould. After gelling has been commenced and the flowable refractory slurry has solidified to such degree that it does not flow even when the shaping mould is inclincd, (the slurry hardened to such degree will hereinafter be referred to as casting mould), the casting mould is removed from the shaping mould and immersed in the hardening water. Since the casting mould is required to have a smooth and flat surface and a high strength, the coarse and fine particles constituting the core of the casting mould are blended so as to obtain the closest-packed structure.

For obtaining a casting mould of such closest-packed structure, it is necessary to ensure that the alcohol contained in the casting mould be dissipated into the hardening water, as the castng mould is particularly low in air-permeability. This can be achieved by decreasing the surface tension of the hardening water to facilitate penetration of the hardening water into the casting mould. To decrease the surface tension, the addition of a surface active agent is effective and usable surface ac- 5 tive agents include anion active agents, cation active agents, nonionic active agents and ampholytic active agents.

Where it is desired to produce a casting mould having a relatively large wall thickness, more coarse particles than in case of the closest-packed structure need to be used for preventing deformation of the casting mould. When such casting mould is large in size, it has good air-permeability but a relatively low strength. In order to increase the strength of such casing mould, a watersoluble silica sol solution is added to the hardening water. Namely, the alcohol formed in the casting mould as a result of hydrolysis of ethyl silicate is substituted by the water-soluble silica sol which is effective for binding tightly the casting mould.

The water-soluble silica sol may be being sold on the market.

For the production of a casting mould which has a special shape and is required to have a high strength, a method is employed in which the casting mould is hardened by use of a hardening water having a surface active agent and a water-soluble silica sol added thereto.

Now, the casting mould producing method of this invention will be illustrated by means of examples.

EXAMPLE 1 l. Powdered refractory material Zircon sand powder Particle size Smaller than 100 mesh 100 percent Smaller than 270 mesh 70 percent 2. Partially hydrolyzed binder Water ratio (Amount of water actually added)/(Theoretical amount of water) 50 percent Composition Ethyl silicate 40 80 percent 1 HCl alcohol 14 percent Water 6 percent 3. Gelling promoting agent 8 percent aqueous solution of ammonium carbonate 4. Hardening water Water (20C.) containing 1 percent of the cation active agent of the formula CH (CH2) N (CH2CH2O)2H 2,000 cc. of the partially hydrolyzed binder was added to 10 kg of the powdered refractory material, to which was further added 70 c.c of the gelling promoting agent, and the mixture was thoroughly stirred to prepare a flowable refractory slurry. This flowable refractory slurry was poured into a shaping mould. The slurry started to gel and became unflowable in about 6 minutes. The flowable refractory slurry having reached such state (casting mould) was removed from the shaping mould and immediately immersed in the hardening water and held therein for about 1 hour, whereby the casting mould was imparted with an extremely high strength (about 70 kg/cm of compressive strength).

one generally (CH CH O) H The casting mould was retrieved from the hardening water and dried overnight at room temperature.

Upper and lower parts of the casting mould produced in the manner described above were bonded together by means of a refractory adhesive and calcined in a muffle furnace at 900C. for about 3 hours. Molten stainless steel was poured into the casting mould maintained at about 800C. The casting thus obtained had a very high dimensional accuracy and a quality equal to that of an investment casting having a smooth and flat surface.

EXAMPLE 2 l. Powdered refractory material 1. Powdered material Chamotte powder Particle size proportion Weight (71) 60 100 mesh 35 200 mesh and smaller 65 2. Partially hydrolyzed binder Water ratio (Amount of water actually added)/(Theoretical amount of water) 70 percent Composition Ethyl silicate 40 80 percent l HCI alcohol 11.6 percent Water 8.4 percent 3. Gelling promoting agent percent aqueous solution of ammonium carbonate 4. Hardening water Water (30C.) containing 1 percent of the nonionic active agent of the formula CH (CH O(CH C- H O);,H 4.000 c.c. of the partially hydrolyzed binder was added to 30 kgs of the powdered refractory material, to which was further added 130 c.c. of the gelling promoting agent, and the mixture was thoroughly stirred. The flowable refractory slurry thus obtained was cast on the surface of a shaping mould and aback sand mould made of CO mould using chamotte sand was superimposed and bonded thereto with pressure. In this case, the thickness of the flowable refractory slurry (the gap between the shaping mould and the back sand mould) was 3 10 mm. Gelling of the flowable refractory slurry began in about 8 minutes. The back sand mould was inverted together with the shaping mould and then the shaping mould was removed. The hardening water was sprayed over the surface ofthe casting mould (facing sand) which had been exposed upon removal of the shaping mould and retained for about 2 minutes. By this treatment, the flowable refractory slurry used for the facing sand was completely hardened. The casting mould was left to stand still overnight and then dried in a drying furnace at 400C.

Upper and lower mould parts of the casting mould produced in the manner described were used in the same casting operation as in Example 1, and a casting was obtained which was high in dimensional accuracy and had a smooth and flat surface.

EXAMPLE 3 l. Powdered refractory material Zircon sand sintered powder and zircon sand powder Particle size proportion Weight (7t) 20 40 mesh 35 4O 100 mesh 20 100 200 mesh 20 200 mesh and smaller 25 2. Partially hydrolyzed binder Water ratio Amount of water actually added/Theoretical amount of water percent Composition Ethyl silicate 40 80.0 percent 1 7c HCI alcohol 1L6 percent Water -8.4 percent 3. Gelling promoting agent 10 percent aqueous solution of ammonium carbonate 4. Hardening water Composition Water (20C.) 50 percent Water-soluble silica sol 50 percent (Silica sol solution prepared by using water as dispersion medium and containing 20 percent of SiO 1,600 cc of the partially hydrolyzed binder was added to 10 kg of the powdered refractory material, to which was further added 32 c.c. of the gelling promoting agent, and the mixture was stirred to prepare a flowable refractory slurry.- The flowable refractory slurry thus prepared was poured into an aluminum shaping mould. The slurry began to gel in about 5 6 minutes after pouring, but in this Example, was left stand still in said shaping mould for about l5 minutes intentionally, to prevent deformation of the casting mould to be produced. Gelling proceeds sufficiently during this period and the possibility of deformation of the casting mould is precluded. The casting mould was removed from the aluminum shaping mould and immediately placed in the hardening water containing the water-soluble silica sol. The alcohol in the casting mould was substituted by the hardening water, with the silica sol penetrating into the casting mould, whereby the strength of said casting mould after drying in air was increased. A testing conducted on a sample piece of the mould provided separately, revealed that the casting mould had a deflective strength of 40 42 kg/cm After drying, upper and lower parts of the casting mould thus produced were assembled in the same manner as in Example 1 and calcined in a gas calcining furnace at 950C. for about 4 hours, and molten stainless cast steel was poured therein. A conventional casting mould (used as a core in the flow passage) has frequently suffered breakage or swell when it is thin and slender, but the casting mould produced in this example was completely free of swell and enabled a beautiful casting to be obtained, with a smooth and flat surface just the same as that of the casting mould.

EXAMPLE 4 l. Powdered refractory material Fused silica Particle size Smaller than 300 mesh percent 2. Partially hydrolyzed binder Water ratio (Amount of water actually added)/(Theoretical amount of water) 60 percent Composition Ethyl silicate 40 80 percent l 74 HCl alcohol 12.8 percent Water 7.2 percent 3. Gelling promoting agent percent aqueous solution of ammonium carbonate 4. Hardening water Composition Water (30C.) 60 percent Water-soluble silica sol 40 percent (silica sol solution prepared by using water as dispersion medium and containing percent of SiO This hardening water had added thereto 1 percent of the nonionic active agent of the formula CH (CH O(CH CH O) H.

1,300 c.c. of the partially hydrolyzed binder was added to 200 g of the powdered refractory material, to which was further added 5 c.c. of the gelling promoting agent, and the mixture was stirred to obtaine a .flowable refractory slurry. This flowable refractory slurry was in the form of cream, since the powdered refractory material used was very small in particle size. The slurry was placed in the cylinder of a pressure injector and injected therethrough into a metallic shaping mould, intended for the production of a precision core, with a pressure of 2 3 kg/cm The metallic shaping mould with the slurry poured therein was immersed in the hardening water for about 3 minutes. The resultant core was removed from the mould while holding said mould immersed in the hardening water.

The core thus produced was held immersed in the hardening water for about 30 minutes and then, retrieved from said hardening water and dried in air.

Thereafter. the core was calcined in a calcining furnace at l,000C. for about l hour and cooled slowly. A testing conducted on a sample piece of the core produced separately, revealed that the core had a deflection strength of 52 kg/cm and was thus extremely high in strength, in this state.

According to the method of this invention, it is possible to produce a casting mould for precision casting, free of defect up to the bottom of a deep groove or hole, which cannot be produced by the conventional method, and therefore. it is possible to obtain casting having a high dimensional accuracy and excellent quality.

Further, the strength of the casting mould is so high that the casting of complicated small-sized precision cores used in the investment casting, etc. can be facilitated. In addition, since the binder used has a shelf life of as long as several months and is highly stable, the method can be operated accurately and brings about a remarkable effect in respect of production control.

ln the conventional method in which the product casting mould is heated rapidly, hardening of the casting mould proceeds unevenly in most cases and it is impossible to heat the entire surface of the casting mould concurrently in the event when the casting mould has a complicated shape, such as a core, with the result that swell or crack occurs in the mould. In the method of this invention, however, since the product casting mould is hardened by use ofa hardening water, hardening of the mould proceeds concurrently from the entire surface, and the method is adapted especially for the production of cores.

What is claimed is:

1. A method for producing a casting mould for use in precision casting comprising preparing a flowable refractory slurry comprising a mixture of a powdered refractory material, a binder obtained by the hydrolysis of ethyl silicate with an amount of water smaller than the theoretical hydrolysis amount of water, and a sufficient amount of a gelling promoting agent sothat gelling will commence is about 6 to 8 minutes after said slurry is poured into a shaping mould; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after said slurry has gelled; immersing said casting mould in a hardening water containing sufficient surface active agent therein to decrease the surface tension of said hardening water to thereby completely harden said casting mould; and then drying and calcining said casting mould to obtain said casting mould.

2. A method for producing casting moulds for use in precision casting according to claim 1, in which the casting mould removed from the shaping mould is immersed in hardening water containing a water-soluble silica sol.

3. A method for producing casting moulds for use in precision casting according to claim 1, in which the casting mould removed from the shaping mould is immersed in hardening water containing a surface active agent and a water-soluble silica sol.

4. The method according to claim 1, wherein the gelling promoting agent is selected from the group consisting of ammonium carbonate, triethanolamine, pyridine and piperidine.

5. The method according to claim 1, wherein said surface active agent is selected from the group consisting of anion active agents, cation active agents, nonionic active agents and ampholytic active agents.

6. The method according to claim 1, wherein said slurry is an alcohol slurry.

7. The method according to claim 1, wherein said refractory material is selected from the group consisting of Zircon sand powder, Chamotte powder, sintered Zircon sand powder and fused silica.

8. The method according to claim 1, wherein said gelling promoting agent is ammonium carbonate.

9. The method according to claim 1, wherein about 1,300 to 2,000 c.c. of said binder is mixed with each 10 kg, of said refractory material.

10. The method according to claim 1, wherein the amount of saiad binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm 11. The method according to claim 1, wherein the amount of water in said binder is about 50 to percent of the theoretical hydrolysis amount of water.

12. The method according to claim 1, wherein said refractory slurry consists essentially of a mixture of said powdered refractory material, said binder, said gelling promoting agent and acidified alcohol.

13. The method according to claim 1, wherein said surface active agent is selected from the group consist- CH (CH N (CH CH O) H or a nonionic active agent of the formula:

14. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry consisting essentially of a mixture of Zircon sand powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing said casting mould in hardening water containing a cationic surface active agent therein to thereby completely harden said casting mould; drying said casting mould; then calcining said casting mould at a temperature of about 900C. to obtain said casting mould useful for precision (CHZCHZCDZH CH (CH N (CH CTI O) 18. The method according to claim 14, wherein said flowable refractory slurry is an alcohol slurry.

19. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry consisting essentially of a mixture of Chamotte powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing said casting mould in hardening water containing a nonionic surface active agent to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 400C. to obtain said casting mould useful for precision casting.

20. The method according to claim 19, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.

21. The method according to claim 19, wherein the amount of binder is sufficient so that said casting mould has a detlectivc strength of at least about 40 kglcm 22. The method according to claim 19, wherein said surface active agent has a formula:

n lzln l lz Hg h 23. The method according to claim 19, wherein said flowable refractory slurry is an alcohol slurry.

24. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry comprising a mixture of Zircon sand sintered powder, Zircon said powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount ofwater, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing the casting mould in hardening water containing a silica sol aqueous solution to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 950C. to obtain said casting mould useful for precision casting.

25. The method according to claim 24, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.

26. The method according to claim 24, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm 27. The method according to claim 24, wherein said flowable refractory slurry is an alcohol slurry.

28. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry of a mixture of fused silica, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing the casting mould in hardening water containing a water-soluble silica sol and a nonionic surface active agent to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 1,00()C. to obtain said casting mould useful for precision cast- 29. The method according to claim 28, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.

30. The method according to claim 28, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm 31. The method according to claim 28, wherein said surface active agent has the formula:

32. The method according to claim 28, wherein said flowable refractory slurry is an alcohol slurry.

33. The method according to claim 7, wherein said refractory slurry consists essentially of a mixture of said powdered refractory material, said binder, said gelling promoting agent and acidified alcohol. 

1. A METHOD FOR PRODUCING A CASTING MOULD FOR USE IN PRECISION CASTING COMPRISING PREPARING A FLOWABLE REFRACTORY SLURRY COMPRISING A MIXTURE OF A POWDERED REFRACTORY MATERIAL, A BINDER OBTAINED BY THE HYDROLYSIS OF ETHYL SILICATE WITH AN AMOUNT OF WATER SMALLER THAN THE THEORETICAL HYDROLYSIS AMOUNT OF WATER, AND SUFFICIENT AMOUNT OF A GELLING PROMOTING AGENT SO THAT GELLING WILL COMMENCE IS ABOUT 6 TO 8 MINUTES AFTER SAID SLURRY IS POURED INTO A SHAPING MOULD; POURING SAID FLOWABLE REFRACTORY SLURRY INTO A SHAPING MOULD; REMOVING THE RESULTANT CASTING MOULD FROM SAID SHAPING MOULD AFTER SAID SLURRY HAS GELLED; IMMERSING SAID CASTING MOULD IN A HARDENING WATER CONTAINING SUFFICIENT SURFACE ACTIVE AGENT THEREIN TO DECREASE THE SURFACE TENSION OF SAID HARDENING WATER TO THEREBY COMPLETELY HARDEN SAID CASTING MOULD, AND THEN DRYING AND CALCINING SAID CASTING MOULD TO OBTAIN SAID CASTING MOULD.
 1. A method for producing a casting mould for use in precision casting comprising preparing a flowable refractory slurry comprising a mixture of a powdered refractory material, a binder obtained by the hydrolysis of ethyl silicate with an amount of water smaller than the theoretical hydrolysis amount of water, and a sufficient amount of a gelling promoting agent so that gelling will commence is about 6 to 8 minutes after said slurry is poured into a shaping mould; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after said slurry has gelled; immersing said casting mould in a hardening water containing sufficient surface active agent thereIn to decrease the surface tension of said hardening water to thereby completely harden said casting mould; and then drying and calcining said casting mould to obtain said casting mould.
 2. A method for producing casting moulds for use in precision casting according to claim 1, in which the casting mould removed from the shaping mould is immersed in hardening water containing a water-soluble silica sol.
 3. A method for producing casting moulds for use in precision casting according to claim 1, in which the casting mould removed from the shaping mould is immersed in hardening water containing a surface active agent and a water-soluble silica sol.
 4. The method according to claim 1, wherein the gelling promoting agent is selected from the group consisting of ammonium carbonate, triethanolamine, pyridine and piperidine.
 5. The method according to claim 1, wherein said surface active agent is selected from the group consisting of anion active agents, cation active agents, nonionic active agents and ampholytic active agents.
 6. The method according to claim 1, wherein said slurry is an alcohol slurry.
 7. The method according to claim 1, wherein said refractory material is selected from the group consisting of Zircon sand powder, Chamotte powder, sintered Zircon sand powder and fused silica.
 8. The method according to claim 1, wherein said gelling promoting agent is ammonium carbonate.
 9. The method according to claim 1, wherein about 1,300 to 2,000 c.c. of said binder is mixed with each 10 kg, of said refractory material.
 10. The method according to claim 1, wherein the amount of said binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm2.
 11. The method according to claim 1, wherein the amount of water in said binder is about 50 to 70 percent of the theoretical hydrolysis amount of water.
 12. The method according to claim 1, wherein said refractory slurry consists essentially of a mixture of said powdered refractory material, said binder, said gelling promoting agent and acidified alcohol.
 13. The method according to claim 1, wherein said surface active agent is selected from the group consisting of a cation active agent of the formula:
 14. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry consisting essentially of a mixture of Zircon sand powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing said casting mould in hardening water containing a cationic surface active agent therein to thereby completely harden said casting mould; drying said casting mould; then calcining said casting mould at a temperature of about 900*C. to obtain said casting mould useful for precision casting.
 15. The method according to claim 14, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.
 16. The method according to claim 14, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm2.
 17. The method according to claim 14, wherein said surface active agent has a formula:
 18. The method according to claim 14, wherein said flowable refractory slurry is an alcohol slurry.
 19. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory sLurry consisting essentially of a mixture of Chamotte powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing said casting mould in hardening water containing a nonionic surface active agent to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 400*C. to obtain said casting mould useful for precision casting.
 20. The method according to claim 19, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.
 21. The method according to claim 19, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm2.
 22. The method according to claim 19, wherein said surface active agent has a formula: CH3(CH2)11O(CH2CH2O)3H
 23. The method according to claim 19, wherein said flowable refractory slurry is an alcohol slurry.
 24. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry comprising a mixture of Zircon sand sintered powder, Zircon said powder, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing the casting mould in hardening water containing a silica sol aqueous solution to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 950*C. to obtain said casting mould useful for precision casting.
 25. The method according to claim 24, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.
 26. The method according to claim 24, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 kg/cm2.
 27. The method according to claim 24, wherein said flowable refractory slurry is an alcohol slurry.
 28. A method for producing a casting mould useful for precision casting comprising preparing a flowable refractory slurry of a mixture of fused silica, a binder obtained by the hydrolysis of ethyl silicate with an amount of water less than the theoretical hydrolysis amount of water, and an aqueous solution of ammonium carbonate; pouring said flowable refractory slurry into a shaping mould; removing the resultant casting mould from said shaping mould after the slurry has gelled; immersing the casting mould in hardening water containing a water-soluble silica sol and a nonionic surface active agent to thereby completely harden said casting mould; drying said casting mould; and calcining said casting mould at a temperature of about 1,000*C. to obtain said casting mould useful for precision casting.
 29. The method according to claim 28, wherein the amount of aqueous solution of ammonium carbonate in said flowable refractory slurry is sufficient so that gelling will commence in about 6 to 8 minutes after said slurry is poured into said shaping mould.
 30. The method according to claim 28, wherein the amount of binder is sufficient so that said casting mould has a deflective strength of at least about 40 KG/CM2.
 31. The method according to claim 28, wherein said surface active agent has the formula: CH3(CH2)11O(CH2CH2O)3H
 32. The method according to claim 28, wherein said flowable refractory slurry is an alcohol slurry. 